Spraying apparatus

ABSTRACT

AN APPARATUS FOR SPRAYING CHEMICALS FROM A VEHICLE. A WATER SUPPLY AND ONE OR MORE CONTAINERS FOR CHEMICALS FORMULATED AS SOLUTIONS OR SUSPENSIONS ARE PROVIDED. THE WATER SUPPLY IS CONNECTED TO THE SPRAY NOZZLES THROUGH A WATER SUPPLY LINE, AND MEANS IS PROVIDED TO PRODUCE A STANDARD PRESSURE IN THE WATER SUPPLY LINE. AT LEAST ONE CHEMICAL SUPPLY LINE IS CONNECTED FROM EACH CHEMICAL CONTAINER TO THE WATER SUPPLY LINE, EACH CHEMICAL SUPPLY LINE BEING PROVIDED WITH MEANS TO PRODUCE AN EXCESSIVE PRESSURE DROP ALONG IT AND PRESSURE RELEASE MEANS TO REDUCE THE FLOW RATE CAUSED BY THIS PRESSURE DROP TO THAT REQUIRE. THE PRESSURE RELEASE MEANS IS ADAPTED TO CONTROL, ACCORDING TO VEHICLE SPEED, THE RESISTANCE TO FLOW SO THAT THE RATE OF FLOW OF CHEMICAL IS PROPORTIONAL TO VEHICLE SPEED.

United States Patent Assistant Examiner-Michael T. Mar Attorney-Wenderoth, Lind & Ponack ABSTRACT: An apparatus for spraying chemicals from a vehicle. A water supply and one or more containers for chemicals formulated as solutions or suspensions are provided. The water supply is connected to the spray nozzles through a water supply line, and means is provided to produce a standard pressure in the water supply line. At least one chemical supply line is connected from each chemical container to the water supply line, each chemical supply line being provided with means to produce an excessive pressure drop along it and pressure release means to reduce the flow rate caused by this pressure drop to that required. The pressure release means is adapted to control, according to vehicle speed, the resistance to flow so that the rate of flow of chemical is proportional to vehicle speed.

HYDRAULIC SUPPLY PATENTEU JUN28 I97! SHEEI 1 BF 5 HYDRAULIC FIG] SUPPLY l INVENTOR I ALEXANDER A. ROSS PATENTED JUN28I9?! $5 sum a or s FIGZ I 25 INVENTOR ALEXANDER A. ROSS ATTORNEY PATENTED JUN28 l97l 3587.971

' sum 3 [1F 5 INVENTOR ALEXANDER A. ROSS ATTOR NE Y:

PATENTEDJUNPSIBYI 3587.971

' v saw u or s 40psi 20-60psu 20psi INVENTOR 44 ALEXANDER A. ROSS ATTORNEY;

PATENTEU JUN28l97l 35 -8 1 SHEEI 5 OF 5 INVENTOR ALEXANDER A. ROSS ATTORNEYS SPRAYING APPARATUS The present invention relates to improvements in apparatus for spraying chemicals from vehicles.

To obtain satisfactory performance from a spray nozzle operated by water pressure only, his desirable that' the nozzle should operate at a pressure close to that for which it is designed. The spray will then spread out to give a fairly uniform band of constant width. The rate at which liquid is discharged is constant, so that the density of the deposit left by the spray is inversely proportional to the speed with which the carrier machine traverses the ground.

The density of liquid deposit on the ground may not itself be of great importance, but the density of deposit of some dissolved or suspended physiologically active substance, such as a herbicide, may be very important. lf a solution or suspension is sprayed at constant pressure from a conventional machine it is therefor necessary thatthis machine traverses the ground at an approximately constant rate near to the optimum.

Some ground spraying operations are carried out from machines whose speed of traverse is very variable, being set by other conditions than optimum use of chemicals. For example, herbicides are sprayed on railway tracks and verges from trains which have a low rate of acceleration or retardation and may be subject to traffic-regulated signal checks. It is-necessary in such cases that spraying be carried out with acceptable efficiency over a wide range of speeds from say 40m.p.h. down to as near as practicable to complete standstill.

To get over this difficulty it has been proposed to supply water to the spray nozzles at a constant rate (volume per unit time) and to force into the water stream concentrated chemical at a rate proportional to train speed. Thus, the spray pattern and width of sprayed swath is maintained constant and the amount of chemical per unit distance traversed is maintained constant, only the diluent (water) density being allowed to vary.

To achieve this desirable result an independently powered pump forces diluent water from a train-mounted supply tank while a separate pump operated from the track-wheels forces in chemical concentrate from another train-mounted supply tank. This metering pump is preferably a piston pump provided with means for varying the stroke, so that its rate of pumping is proportional to train speed but the constant of proportionality can be varied at the choice of the operator.

A disadvantage of this system is that massive and bulky pumps and drives are necessary for what is substantially a flow-control requirement. This becomes serious if several chemicals are required at choice, together or separately, each needing its own track-driven metering pump.

it has now been found that a more convenient and cheaper arrangement to achieve the desired result of metering chemicals into a water stream at a rate proportional to vehicle speed is to supply, in the liquid chemical concentrate line, a pressure difference which could produce an excessive flow in the pipes along which the pressure falls and to restrict this flow by controlling devices. These devices, operated or controlled by the track or land wheels, or axles rotating proportionately thereto, either reduce the operative pressure to that required to produce the desired flow, or vary the resistance of athrottle inserted in the conducting pipes so that the desired flow is produced by the original pressure.

Accordingly the present invention is for an apparatus for spraying chemicals from a vehicle comprising a water supply and one or more containers for chemicals formulated as solutions or suspensions, a connection from the water supply to the spray nozzles, hereinafter called the water supply line. means to produce a standard pressure in the water supply line, at least one connection from each chemical container to the water supply line hereinafter called the chemical supply line, each chemical supply line being provided with means to produce an excessive pressure drop along it and pressure release means to reduce the flow rate caused by this pressure drop to that required, said pressure release means being adapted to control, according to vehicle speed, an adjustable valve means in the chemical supply line, such as a throttle inserted in the chemical supply line or a pressure reducing valve which limits the pressure drop across a fixed resistance so that the rate of flow of chemical is proportional to vehicle speed.

in one embodiment of the invention the chemical supply line pressure release means produces a standard pressure, and the control of flow of chemical is achieved by means of a variable resistance throttle.

In another embodiment of the invention, a fixed resistance throttle is used, and the control offlow of chemical is obtained by variable means for the variation of the pressure difference between the chemical supply line and the water supply line.

When using a variable resistance throttle, dependence on a constant pressure difference to drive the chemical can be. avoided, by inserting in the chemical supply line a fixed resistance throttle with pressure recording means for recording the pressure difference across it. A variable resistance throttle is inserted in series with the fixed resistance throttle and the functional area of this variable throttle must be automatically controlled so that the pressure difference across the fixed throttle is systematically related to the vehicle speed.

In the embodiment of the invention involving the use of a variable resistance throttle, means of relating the functional area of the variable throttle to the train speed can be either mechanical, making use of a lever system operated by a cen trifugal governor, or electrical, using current generated by a dynamo driven by the train wheels. Several systems of electrical servomechanisms are known in the art and can be adapted to this purpose. They have the advantage that it is simple to build into electrical mechanisms any desired relationship between controlling speed and controlled functional are of the variable throttle by adjustment of resistances, capacitances etc. in the circuit. Such adaptability is necessary because the variable throttle is most conveniently made in two parts with linear movement of one only of its component members. The relationship between flow rate and relative position of these members is not necessarily linear so that final adjustment must be made by calibration to ensure that flow rate is proportional to train speed.

The system of metering chemical proportionately to distance travelled into a diluent volume flowing at constant rate has also advantages in agricultural spray machinery although this is not normally required to operate over so wide a range of land speed. It enables more precise dosage per acre to be achieved. it also enables more-efficient use to be made of expensive corrosion-resistant materials and facilitates cleaning, since the main water tank and supply line are not con-' taminated.

In an agricultural machine however the more sophisticated electrical servomechanisms may not be acceptable on grounds of cost; in this case the connection between land speed and controlling means is preferably mechanical.

in the embodiment of the invention relying on variation of able area or a series of orifices in at least one plate so arranged that the resistance can be changed by introducing orifices of different areas or a different number of orifices into the flow line. The orifices preferably consist of holes in a thin plate of hard metal since the fiow rate is then proportional to squareroot of pressure difference over a wide range of areas or of numbers of orifices.

The pressure reducing valve is of conventional design in which a chamber is separated from the atmosphere by a diaphragm which is restrained by a spring and activates an.

inlet valve. Liquid can only enter the chamber when the pres sure therein falls belowa value controlled by the spring setting. Liquid is therefore passed forward at a constant pres-- Connection between vehicle speed and pressure control can be entirely mechanical, electromechanical or by hydraulic pressure. Only in the first case is it necessary for the energy for control to be supplied by the speed sensor. In the other cases it is supplied by an external source of electrical or hydraulic pressure. The power-assisted methods are more reliable than the purely mechanical method.

Solely by way of illustration various embodiments of the invention are shown in the accompanying drawings. The essential features of the apparatus are shown in these drawings, but purely conventional features are not shown.

FIG. 1 shows an electromechanical arrangement for the control of flow using a variable resistance throttle in the form ofa variable area orifice.

FIG. 2 shows a mechanical arrangement for the control of flow using a variable resistance throttle in the form of a varia ble area orifice.

FIG. 3 shows a modified arrangement of FIG. 2 with one stage of power amplification.

FIG. 4 shows an electromechanical arrangement for the control of flow using a means for variation of pressure difference including power amplification.

FIG. 5 shows a mechanical arrangement for the control of flow using a means for variation of pressure difference including power amplification.

In FIG. 1, an unidirectional electrical current with voltage in proportion to speed is generated in the conventional speedvoltage transducer 1, the rotor of which is driven by the track wheels. This current is fed to the controllable potentiometer 2. The output voltage, proportional to speed but with a constant of proportionality selected by adjustment of 2, is fed to one coil ofthe voltage comparison device 3.

Imbalance in the voltage comparison device 3 operates one oftwo contacts which cause the opening of one set of valves in the electrohydraulic converter 4 connected to terminals 4', thereby allowing oil from the hydraulic supply to exert pres sure on one side of the hydraulic ram 5.

The movement of the ram 5 operates a variable area orifice 6 in the chemical supply line and also operates the positional feedback unit 7 which supplies a unidirectional voltage from, for example, a battery, to another coil in the voltage comparison device 3. The two coils in the voltage comparison device are generally arranged as opposed windings on an electromagnet, the resultant magnetization of which operates a simple electrical relay to control the two valves in the hydraulic supply.

When the voltage from the proportional'dosage rate control 2 and the voltage from the positional feedback unit 7 are balanced the control mechanism is at rest with orifice 6 set to pass the amount'of liquid required to suit the input voltage from 1.

The chemical supply 8 is via a centrifugal pump 8 and pressure reducing valve 9 through the variable orifice 6 to a point in the water supply line. The spray outlets are represented for convenience as a single nozzle 10.

The water supply 11 is via centrifugal pump 11' and pressure reducing valve I2 to a junction situated before the spray nozzle where it meets and mixes with the chemical supply.

The transducer 1 supplies a voltage bearing a fixed relationship to the rate of revolution of the track wheels and hence to the vehicle speed. The device 2 transmits a chosen fraction of this voltage to 3. The movement of the ram 5 rigidly attached to the moving member of the variable orifice plate 6 controls both the chemical flow rate and the voltage supplied by 7. The system is in a steady condition when the two voltages supplied to 3 are in balance. It is necessary that the rate of flow of chemical be proportional to the land speed and this will be achieved if all the intermediate quantities are proportional to one another. The latter condition is however not strictly necessary. For example, if the voltage generated by 2 were proportional to the square of the land speed and that supplied by 7 were proportional to the square of the chemical flow rate, the desired linear proportionality between land speed and flow rate would result. It will however be generally more convenient to adjust each component of the system so that each variable is linearly proportional to the next in sequence. The linearity between land speed and voltage produced ml is achieved by appropriate winding of the generator. The linearity between voltage in 7 and flow rate through 6 is adjusted by means of the plurality of variable resistors shown in 7.

A completely mechanical connector is now described with reference to FIG. 2.

A centrifugal governor 13 of conventional design with a compression spring 14 is so adjusted that the displacement of the moving member 15 of the governor up the axle from its zero position is approximately proportional to the speed of revolution over the range of speed desired in operation. The axle is mechanically driven by belt, chain, gears or torsion cable from the track or land wheels of the vehicle. The up and down movement of 15 is transferred, via the bellcrank l6 pivoted at 17, to a right and left movement of the connector 18 which can be rotatively fixed at 19 at any desired part of the quadrant 20 which is integral with the arm 21 and pivoted about 22. The arm 21 is rotatably attached at its other end to the moving diaphragm 23 of the combined orifice plate 24.

The combined orifice plate 24 is arranged in a chemical supply system as shown in FIG. I where the orifice plate 24 replaces the variable orifice 6 in FIG. 1.

As land speed increases, 15 moves upwards. This movement is translated, with a constant of proportionality controlled by the position of 19 on 20, into an upward movement of the diaphragm 23 containing the orifice 25 with respect to the fixed hole 26, thus increasing the flow of chemical.

It is again in principle not necessary that all movements be linearly proportional, provided that each varies as some simple power of its precursor and that this power is at another stage inverted. It will however be generally more convenient to adjust each connecting device in the series so that each quantity is linearly proportional to its precursor. Linear proportionality between flow rate and displacement of the moving orifice diaphragm from its zero position is achieved by adjusting the contour of one of the orifices, e.g., the orifice 25 in the moving diaphragm. Adequate linear proportionality between the intermediate displacement is secured by arranging that the lever arms are all long enough for the angular displacement to be small.

FIG. 3 shows a modified arrangement of FIG. 2 in which the power to operate the variable area orifice is provided by oil pressure activating a hydraulic ram connected to the moveable member of the gate valve, the oil pressure being connected only when there is imbalance between the governor position and the gate-valve position.

A is a conventional centrifugal governor rotating in bearings fixed to the vehicle chassis and driven by belt, chain, gear or torsion cable from the track or land wheels of the vehicle. This directly moves the toothed arc-shaped arm, B, about a bearing, C, at the center of the arc. The teeth on B engage with those of a wheel, D, mounted on an axle in bearings fixed to the vehicle chassis. This wheel turns both a pointer on a visual speed indicator scale and an insulated metal member, E, which can make contact with either part F or F of an interrupted circular metal member, mounted on an insulated wheel which is on the same axle as a toothed wheel, G, this axle being collinear with, but not connected to, the axle of the wheel, D. The metal members, F and F,, are separated in two places and an insulated stop X blocks one gap so that the member, E, can make contact with either F or F,. By conventional electrical circuit connection with a source of electrical power, contact between E and one of F and F opens a solenoid-operated valve to allow oil to enter one side of the hydraulic ram, H. Contact between E and the other of F and F opens an opposite valve. The ram is therefore caused to move up or down according to whether the wheel D is in advance or arrear of wheel G and is nonoperative only when these wheels are in alignment. in the noncontact position the member, E, lies in the insulated space between the two halves of F.

The ram is connected directly to the moving member of the variable-area orifice, J, and, by cams to be described below, to the wheel G, in such a way that C is caused to copy the movement ofD but with power supplied by the oil pump serving the ram.

A link, K, the functional length of which is the radius of the toothed arc member, LM, is rotatably mounted at N to a pro-- jection from the piston of the ram and at P to a toothed wheel engaging with LM. L is a bearing fixed to the vehicle chassis and M is a rotatable connection to a second link member, Q, similarly engaging at R with a second toothed arc member, ST. ST rotates about a bearing S fixed to the chassis and carries a second toothed arc member TU rigidly attached at T and having its center at S. This engages with the above-mentioned toothed wheel, G.

If the movement of the toothed wheels, P and R, in their engaging arcs, is locked, leaving the links X and Q free to rotate about either end in so far as other connections allow, upward movement of the ram connection N acting through K, Q and TU drives the wheel G in a clockwise direction. This is in the same direction as D is turned by an increase in vehicle speed. The rarn drives the wheel G in the same direction as D is driven by the vehicle acceleration and ceases to drive when contact between E and F is broken. Upward movement of the ram also opens the variable area orifice J and allows more chemical to pass. The rate of supply of chemical can thus be made proportional to the vehicle speed.

When the apparatus is operating at a steady speed, adjustment of the locations of P and R or ST and LM at which the links K and Q engage can be made without moving ST or LM since M is the center of arc ST and N of LM. This adjustment is made by rotating the toothed wheels in P and R. If these are now locked in new locations, the ratio of movement of the ram to movement of wheel G can be altered, this ratio being proportional to LPXSR. These variables enable the operator to change at agricultural will the total rate of chemical supplied per unit length of track. In practice one of these is manually set according to the desired area dosage of the chemical in use. The other can be altered at will according to the width being sprayed. Locking of the wheels P and R is done by a turn-screw fixing their axles against the bearings in MP and MR. Slight movement of the toothed wheels in the toothed racks, LM and ST, provides the necessary friction. If, as in an agricultural sprayer, there is no need for rapid adjustment of width of swathe sprayed, one of these control units, e.g., LMQR, can be omitted, leaving K to engage direct with SP, through wheel P.

The object of this design is to enable a centrifugal governor having feeble power to exert powerful but exact control over the variable orifice gate with provision for variation in the ratio of movements. The power is supplied in this example by oil pressure in a ram directly connected to the orifice. The electrical contact system inserted between D and G enables the former to control the movements of the latter, although power to move G is supplied from N. It is evident that other conventional means of power amplification could be used. For example a double capstan amplifier could enable D to control G with external power supplied directly to G. G would then drive N instead of the reverse. Other electrical or hydraulic servomechanisms are well known which could serve the same function as the capstan in this case.

The mechanism'described can be made to operate satisfac torily over a wide range of speeds and dosages, but, owing to play in the link drives, it must become unserviceable at very low speeds or very low dosages when P and R are brought near to L and S. If either P or R are brought fully to the zero position, N becomes fixed but G is free to rotate and the ram shaft could therefore be subject to destructive strain. Self damage is avoided by fixing springs, V and W, joining M to H and T to H to pull the arms ST, LM downwards when they are not otherwise restrained. Also electrical contacts can be introduced near S and L so that they operate on the oil valves and force J to the. zero position when these contacts are made. in effect this enables a very low swathe width setting to be automatically classed as zero.

At very low speeds control becomes erratic. It is preferable to overdose at these speeds. An additional electrical contact near T on UT takes over from the EF contact system when ST moves near to its lower limit and holds ST at a point above the lower limit. If, either link K moves to point L or link 0 moves to point S additional electrical contacts override the contact near T allowing ST to reach zero.

In order to reduce the effect of swaying and jolting of the vehicle on the serviceablity of the device, the members STU and LM are preferably counterbalanced so that their centers of gravity coincide with their fulcra, S and L. The above-mentioned springs attached to J and M eliminate backlash in these moving parts and help to reduce wear.

in FIG. 4, 30 is a centrifugal governor operated by belt, chain, gear or torsion cable from the track or land wheels of the vehicle. Change of speed moves a toothed arm 31 about a pivot 32 and conveys this movement via a toothed wheel 33 to the wiper arm 34 of a potentiometer 35, the resistance of which is built into the form ofa circle with a gap. An external source of voltage is applied across the gap. One side of the gap and the connection to the wiper arm are connected to the units described below, supplying to these units a voltage which is related to vehicle speed. This relationship can be made of any desired simple mathematical form by adjustment to the resistance winding in the potentiometer.

A second similar potentiometer 36 has its wiper arm 37 operated by a reversible motor 38 of any desired power. It is simultaneously connected via a screw-threaded axle 39, to one end of the control spring 40 of the pressure reducing valve 41.

The variable voltages supplied by the potentiometers, 35 and 36, are set in opposition in series with a two-way relay which controls the electrical supply to the reversible motor 38. The only stable position of the wiper arm 37 on 36 is therefore that at which the variable voltage matches that set by the wiper arm 34 on 35. This setting is determined by the vehicle speed and in this way the energy of the motor 38 forces wiper arm 37 also to accommodate to vehicle speed.

In so doing it adjusts the pressure, controlled by the pressure reducing valve 41 at which chemical concentrate is presented to the throttle, 42, the resistance of which has been selected through which it is passed-into the pipeline supplying water at a pressure controlled by the fixed pressure reducing valve, 43, to the spray nozzles 44. Chemical concentrate comes from a supply tank, not shown, through pipe 45 and a pump. Water comes through pipe 46 and a pump. These pumps raise the pressure to higher values than are required so that the pressure reducing valves 41 and 43 can reduce to that required.

Since the primary object of control'of pressure is to control the volume rate of fiow of chemical concentrate into the water, it is the pressure difference between chemical concentrate and diluent water which it is particularly desired to control by the pressure reducing valve 41. it therefore ensures greater accuracy if the diaphragm of the valve 41 is backed not by atmosphere but by diluent water from a point on the water pipeline between the pressure reducing valve 43 and th point of entry of chemical concentrate.

The wiper arm 37 is forced to follow exactly the motion of wiper arm 34, not with regard to position with regard to electrical potential.

In order to set the apparatus so that flow rate is proportional to vehicle speed, adjustment is made in the wiring of the potentiometer 36. Each potentiometer is made up of a series of equally spaced contact studs, with resistance wire coiled between them. Potentiometer 35 is first wired up on an equal increment basis. The wiring of potentiometer 36 is at this stage extended as a separate mounting. Motor 38 is removed. A chosen setting of 34 on 35 is made corresponding to a known vehicle speed. 39 is manually altered until the flow rate desired at this speed is achieved. A sliding contact is made on the extended wire of potentiometer 36 until the relay is nonoperating. This point on the wire is then connected to the stud lying under 37. The process is then repeated at a high speed and flow rate until the potentiometer 36 is assembled with the correct resistance intervals.

In FIG. is illustrated an arrangement where the power to force the spring of the pressure regulator to follow the movement of the centrifugal governor is supplied hydraulically,- where the members 30 and 40 to 46 inclusive refer to parts having the same function as in FIG. 4.

Through conventional pivots and arms the movement of the governor slider is conveyed to a member 47 lying between two spring-loaded levers operating valves 48 and 49 in a hydraulic system, one supplying oil through flexible tubes to the cylinder 50 and the other withdrawing oil therefrom. The oil in cylinder 50 forces movement of a piston rigidly mounted to the valves 48 and 49 and tothe top of the spring 40 which controls the pressure regulator 41. From 41 onwards, function is as in FIG. 4.

It will be seen that downward movement of 47 due to increase in vehicle speed produces downward movement of 48 and 49 until 47 is again in the neutral position between thm. The oil pressure therefore forces the end of the spring 40 to follow the movement of the vehicle speed sensor 47 and in so doing causes the pressure supplied to the orifice 42, and therefore the chemical flow rate, to increase. ln this device the diaphragm of the pressure regulator 41 is shown backed, not by atmosphere, but by water pressure through pipe 51 and chamber 52. The assembly therefore ensures that the pressure drop across the orifice 42 is directly controlled by the governor 30.

As in the case of FIG. 4, it is necessary to arrange that the desired flow rates are obtained at all vehicle speeds, but one cannot do this so simply in absence of the electrical resistance variable. It is necessary to choose the spring 40 of suitable characteristics, making this up if necessary from a group of springs of different length, which come into action at different stages of travel of the compressing member.

lclaim:

1. An apparatus for spraying chemicals from a vehicle comprising a water supply; at least one container for a chemical formulation which is a solution or a suspension; a water supply line connected to said water supply; means in said water supply line for creating a standard pressure in said water supply line; a chemical supply line connected between said container and said water supply line downstream of said pressure creating means; means in said chemical supply line for creating therein a pressure in excess of said standard pressure; and adjustable valve means in said chemical supply line, and control means coupled to said adjustable valve means for adjusting said valve means to vary the flow of the chemical formulation in said chemical supply line in proportion to the speed of the vehicle and for reducing the pressure .to a pres sure no lower than the said standard pressure.

2. An apparatus as claimed in claim 1, wherein said means in said chemical supply line for varying the How comprises a pressure reducing valve and means defining a variable area orifice, and control means coupled to said orifice defining means for varying the orifice in accordance with the speed of the vehicle.

3. An apparatus as claimed in claim 2, in which said control means includes a centrifugal governor rotatable in proportion to the speed of the vehicle.

4. An apparatus as claimed in claim 2, in which said control means includes an electrical servosystem for producing a signal in proportion to the speed of the vehicle.

5. An apparatus as claimed in claim 2, in which said means defining a variable area orifice comprises a first fixed plate having a first aperture, and a second movable plate having a second aperture and coupled to said control means, said second plate being movable past said first plate to move said second aperture linearl past said first a erture 6. An apparatus as c aimed in claim m which said control means includes a hydraulic ram connected to said second plate.

7. An apparatus as claimed in claim 1 in which said means in said chemical supply line for varying the flow comprises a fixed resistance throttle and a variable pressure reducing means, and control means coupled to said variable pressure reducing means for varying the variable pressure reducing means in accordance with the speed of the vehicle.

8. An apparatus as claimed in claim 7 in which said fixed resistance throttle comprises means defining a variable area orifice and including means for fixing the area of the orifice prior to use of the apparatus.

9. An apparatus as claimed in claim 8, in which said fixed resistance throttle comprises at least one plate having a series of apertures therein and means for adjusting the position of said plate for positioning the plate in a fixed position in said chemical supply line for positioning at least one of the apertures in said chemical supply line prior to use of the apparatus.

10. An apparatus as claimed in claim 7, in which said variable pressure reducing means is further connected by a pressure transmitting connection with said water supply line and said control means includes means for varying the pressure difference between the water supply line and the chemical supply line and changing said variable pressure reducing means in response thereto.

11. An apparatus as claimed in claim 7, in which said variable pressure reducing means is a variable pressure reducing valve, and said control means is mechanical control means.

12. An apparatus as claimed in claim 7, in which said variable pressure reducing means is a variable pressure reducing valve, and said control means is electrical control means. 

